On re-reading the original question, I might not has answered the intended question. I addressed the quote in the email: "At high enough frequencies (we do 18 GHZ on rogers) the soldermask changes the impedance of the line." Soldermask does impact CHARACTERISTIC impedance, especially on tightly coupled differential pairs. After the quote above, the question that was asked but not answered by me was: "Is the loss due to the soldermask coating greater than the skin effect loss at very high frequencies?" It was not my intent to comment on whether Soldermask coating caused more loss than skin effect loss at any frequency. My apologies for any confusion. While the paper quoted below is a very good paper on conductor loss, I think Richard needs to look further for loss due to soldermask. Aubrey Sparkman=20 Enterprise Engineering Signal Integrity Team Dell, Inc.=20 Aubrey_Sparkman@xxxxxxxx=20 (512) 723-3592 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of AmateurND@xxxxxxx Sent: Monday, February 21, 2005 3:59 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Skin Effect, Au, and Cu =20 Good day. There is a paper written by James Rautio (Sonnet Software) that might provide some answers. "An Investigation of Microstrip Conductor Loss." =20 It can be downloaded at _http://www.sonnetusa.com/support/publications.asp_ (http://www.sonnetusa.com/support/publications.asp)=20 =20 Michael =20 =20 In a message dated 2/21/05 2:34:36 PM Central Standard Time, Aubrey_Sparkman@xxxxxxxx writes: Soldermask changes the impedance (especially tightly coupled diff pair) for lower frequencies too, just not as significant at low impedance single ended traces. It's less of a series (skin effect) phenomena; did you remember to consider the impact of dielectric constant on impedance.... Aubrey Sparkman=3D20 Enterprise Engineering Signal Integrity Team Dell, Inc.=3D20 Aubrey_Sparkman@xxxxxxxx=3D20 (512) 723-3592 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu